Muffler



March 26, 194D. G. HECTOR ET AL MUFFLER Filed June 23, 1937 3 Sheets-Sheet l A fro/@vers- /N VENTO/25 MMG/.ff

March 26, 1940. L. G. HECTOR Er A1.

MUFFLER Filed June 23, 1957 3 Sheets-Sheet 2 March 26, 1940.

L. G. HECTOR El' AL MUFFLER Filed June 23, 1937 3 lSheets-Sheet 5 n l ll' Q 'a E lf I f| :':l: E 'Ik I 'JIP g @Us I IIIII o IIIIP-f QQ QQ' l Q Patented Mar. '26, 1940 vPATENT OFFICE MUFFLER Luther Grant Hector, Buffalo, and Howard L. Schultz, Cassadaga, N. Y., assignors to Buffalo Pressed Steel Company, Inc., Buffalo, N. Y.

Application June 23, 1937, Serial No. 149,900

17 Claims.

This invention relates to improvements in mufllers or silencers of the kind commonly used in connection with the silencing of the exhaust of internal combustion engines.

One of the objects of this invention is to provide a muffler of the. reverse flow type of improved construction in which gas pressure pulses are broken up into a plurality of parts out of phase with each other for the purpose of equalizing the flow of gas through the'muier. I t is also an object of this invention to provide a mufller of this kind in which the gases are discharged into the muffler housing at different portions of the housing so that gas pressure pulses entering the housing are broken up into a plurality of parts which travel through different distances in the housing to a discharge conduit.

Another object of this invention is to provide a muffler with a housing having inlet and discharge conduits extending into the same and having the inlet conduit provided with discharge openings located at intervals lengthwise thereof and also having the discharge conduit provided with a receiving opening for gases from the chamber which is located at different distances from the openings in the inlet conduit. It is also an object of this invention to provide a mufller in which the inlet duct is provided with openings at intervals lengthwise thereof and in which a discharge conduit is provided having a high frequency acoustic chamber associated therewith. Another object of the invention is to provide a muffler with a relatively large expansion and equalizing chamber into which gases are discharged at different points lengthwise thereof and from which gases are discharged at a point located at different distances from the points of entrance to the chamber, to even out the rate of fluctuation of pressure as rapidly as possible with the minimum of turbulence.

Other objects of this invention will appear from the following description and claims.

In the accompanying drawings Fig. 1 is a longitudinal sectionalr view of a muiller embodying this invention, the section betion, the section being taken through the inlet Y conduit of the muffler.

Fig. 4 is a. fragmentary transverse section thereofv on lim;- 4-4, 3. l

Fig. 5 is a longitudinal sectional View of a mufller of modified construction.

Fig. 6 is a transverse section thereof, on line 6 6, Fig. 5.

Fig. 'l is a longitudinal sectional view of the muffler of still another modified form.

Fig. 8 is a fragmentary longitudinal sectional view of a muffler of still another modified form, the section being taken mainly through the inlet unit of the muffler.

` The mutlier is provided with a housing which may be of any suitable or desired form, that shown as employed on all of the mufers illustrated, including an outer shell A and inlet and discharge heads B and C, the inlet head being provided with a flanged inlet opening b and the discharge head being provided with a similar discharge opening c. In all of the mufllers shown, D represents a duct suitably secured to the flange surrounding the inlet opening and to which an exhaust pipe (not shown) of an engine may be connected and E represents a duct suitably secured to the ilange surrounding the discharge opening of the housing and to which the usual tail pipe (not shown) may be connected. In all of the forms shown, the inlet duct D extends into the interior of the housing and is contracted or reduced in diameter, as shown at d for connection with an inlet conduit within the muffler. All of these parts are commonly used in mufllers and of themselves constitute no part of this invention and may obviously be of any other suitable construction.

Referring to Figs. 1 and 2, I0 represents an inlet conduit which is provided with perforations I l extending throughout a substantial part of the length of the inlet conduit. These perforations may be of any suitable or desired form, for example, in the form of longitudinal slits formed in the conduit I0 andhaving a portion of the metal at one side of each slit forced away from the surface of the conduit, for example, outwardly as clearly shown'in Fig. 2. to form a louver I2 for each opening or perforation. One end of the conduit I0 is connected withI the inlet of the mufller housing, for example,I by securing the same about the reduced part d of the duct D, and the other end of the conduit is preferably closed by means of a suitable cap or flanged disk I4, or any other means for closing or partly closing the end of the inlet conduit may be employed.

I6 represents a discharge conduit which'is connected at one end withthe dischargeduct E of the muztilerv and whichiextends into the housing of the mufllerpreferably substantially parallel to the inlet duct IIJ. The other end of the discharge conduit is open to receive gases from the interior of the housing of the mulller and preferably this open end of the discharge conduit is arranged near the front or inlet end of the muler housing.

We have found that by discharging a gas pressure pulse entering the inlet conduit III at difierentvdistances lengthwise of the conduit, and consequently, at different distances from the open end of the discharge conduit I6, a decided equalizing of the flow of gases through the discharge conduit and tail pipe of the muler results. Consequently, by arranging the perforations II in groups at different distances lengthwise of the inlet conduit, the gases discharged from the group of perforations nearest to the open endl of the discharge conduit I6 will obviously reach the receiving end of the discharge conduit sooner than those parts of the pressure pulse which are discharged through another group of perforations farther removed from the receiving end ofthe discharge conduit I6. Consequently, by means of this arrangement, a gas pressure pulse entering the inlet conduit I 0 may be divided into as many dil-ferent parts as there are discharge openings orperforations disposed at different distances from the inlet end of the discharge duct I6 and theselseveral parts of each pressure pulse will, consequently, pass through the discharge conduit I6 out of phase with each other. This results in a decided equalizing of the flow of gas through the discharge conduit, which in turn results in less resistance to the flow of gas through the discharge conduit, and consequently, in less back pressure in the mulller. By providing the housing of the mufller with a volume materially greater than the combined volume of the inlet and discharge ducts, a further equalizing of the fiowof gas in the discharge conduit I 6 results and also this chamber serves to, reduce the intensity of sound waves, particularly those of low frequency.

While a muiller as thus far described has features of superiority over muillers heretofore constructed, yet certain renements of this construction may be incorporated in the mulller, if desirecl. For example, it has been found that if the gases discharged through the openings or apertures in the inlet conduit impinge directly against the mufller housing, certain shell noises result which, however, can be readily avoided by arranging about the openings or apertures in the inlet conduit suitable sheet metal, members or parts in such a manner that ,the gases discharged through the openings or apertures will impinge against these sheet metal members. Intermediate shells of various types Amay be provided for this purpose, and in the construction shown in Figs. 1 and 2, the intermediate shell surrounding the apertures or openings in the inlet conduit I0 is in the form of a plurality of short cylindrical members or shell parts I8, each of which has a contracted portion or sleeve I9. When outwardly extending louvers I2 are used on the inlet conduit, the conduit is preferably also provided with annular outwardly extending beads or portions 20 to which the contracted portions I9 of the intermediate shell members I8 may be secured so that the portions I9 may, during the assembly of the muliler, be slid lengthwise of the conduit III overthe outer edges of the louvers I2. I'he shell parts I8 may be secured to the conduit III in any' suitable manner, for example, by means of welding, as indicated at 2I.

It will be noted that by means of the construction described, one end of each of the shell parts I8 opens into the interior of the muiller housing, and consequently, gases and sound waves discharged through a group of openings or perforations in the inlet conduit I0 will be discharged into the interior of the housing through an open end of the corresponding shell part I8 and similar gases discharged' through other groups of openings or perfo-rations in the conduit I0 will be dicharged through the open ends of the other shell parts I8 at intervals lengthwise of the conduit I 0. Consequently, a pressure pulse entering the mufller will, by means of the construction shown in Fig.l l, be broken up into three separate pulses which are discharged into the interior of the housing of the muiiler at different distances from the open end of the discharge conduit I6 and will, consequently, enter this conduit in the form of three separate and reduced pressure pulsations, all out of phase with each other. Furthermore, because of the relatively large volume of the interior of the muffler housing, which causes this housing to act as an expansion and equalizing chamber, the parts of vthe pressure pulsations entering the discharge conduit I6 will be very much reduced in intensity as compared with the parts of such pressure pulsations which pass through the open ends of the shell parts I8.

In Figs. 3 and 4, we have shown a modified construction of the inlet unit of the mufiler ln which the perforate portions of the, inner conduit 24 are enclosed by an intermediate shell 25 of single piece construction in whichportions of the intermediate shell are provided with arcuate slits and in which portions 26 of the intermediate shell at one side of the slits are bent or pressed in contact with the conduit 24 and suitably welded or otherwise secured thereto, thus leaving the portions 2'I at the other sides of the slits open to discharge gases into the interior of the muffler housing. This construction also forms openings 28 between the depressed portions 26 so that gases discharged through a group of perforations in the conduit 24 may pass either in one direction through the open end 2'I of a part of the intermediate shell, or in the other direction through the channels 28. In this manner, a further splitting up of the gas pulses results and the intermediate shell may be made of a single cylindrical piece. In this construction, as well as the one shown in Figs. 1 and 2, the intermediate shell parts about the perforations cause the gases discharged through the perforations to impinge therewith and thus avoid the shell noises which would otherwise result.

As shown in Fig. 1, the inner open end of the discharge conduit I6 is cut at an angle, thus forming an open end 30 of larger cross sectional area than if the conduit were cut perpendicular to its length. This facilitates the entrance of gas into the conduit. Furthermore, the conduit is preferably, though not necessarily, provided near the open end thereof with a group of perforations or openings 3 I through which gases and sound waves may pass from the interior of the muler housing. These perforations have the advantage of providing an entrance into the discharge conduit of materially greater combined cross section and this reduces the resistance to the fiow of gases into the discharge conduit. Furthermore, gases and sound waves entering the perforatlons 3| will in general be out of phase with those entering the open end 30 of the conduit so that area than that of the conduit.'

' more effective.

further equalization of gas pulses and some silencing of sound waves will result.

We have found that in a muffler of the general type described in which the gas pulses are broken up so as to enter the discharge conduit in separate parts out of phase with each other and in which a 'large expansion chamber is provided about the inlet and discharge conduits, the gas pressure fluctuations and sound waves entering the discharge conduit are of such nature as to be more efficiently operated upon by an acoustical transmission system with high attenuation for high frequencies, built as a part of the outlet conduit, than in the case with the gas pulses and sound Waves which initially enter the muffler. We have, consequently, found that by the provision of a high frequency acoustic train in connection with the discharge conduit, noises of the exhaust can be quieted to an unusual degree and also a further equalizing of the flow of gases through the discharge conduit and tail pipe results and this in turn results in a decreased back pressure in the muffler. The high frequency acoustic train used in connection with the discharge conduit may be of any suitable or desired form. In the construction illustrated, we have provided the discharge conduit with groups of perforations or openings 34, 35and 36 which may be enclosed by any suitable or well known type of intermediate shell. By way of example, we have shown an intermediate shell 33, which may be supported from the discharge conduit I6 in any suitable manner, for example, by means of transverse baffles or partitions 3l, 38 and 39 which form with the discharge conduit a pair of high frequency resonator chambers 40 and 4I.

It has been found that the silencing of the mufller may be still further improved by providing in the discharge conduit I5 a suitable restriction capable of holding back to a slight extent the gas pressure fluctuations entering the discharge conduit I6. In the construction illustrated, we have provided between the groups of perforations 34 and 35 a restricting sleeve 43 which may have a flange 44 suitably welded or otherwise secured to the conduit i6. This restriction 43 has the further function of causing larger proportions of gases and sound waves to flow through the perforations 34 into the high frequency resonator chamber 40, and then back into the discharge conduit through the apertures 35, than would be the case, if the restriction 43 were not provided. The restriction, therefore7 serves the double purpose of slightly holding back surges or pulses of gases and also of making the high frequency resonator chamber 40 Other means for slightly restricting the flow of gases through the discharge conduit may, of course, be employed, or if desired, this restriction may be entirely omitted.

In the muffler shown in Figs. 5 and 6, a modified form of inlet unit is provided. In this construction, the inlet conduit is provided with two groups of perforations 5l andy 52 and these perforate portions of the conduit are surrounded by. an intermediate shell 53 supported from the conduit 58 by means of transverse baffles 54, 55 and 5S. The baffle 55 may be substantially imperforate and the baffles 54 and 55 may be provided with suitable openings such,v for example, as arcuate slots 51 and 58, see Fig. 6. The parts of the gas pulses discharged through the perforations 5l pass into the interior of the muffler housing through the openings or slots 5i cf the head 54 which is adjacent to the inlet end of the discharge conduit 59 and the gases discharged through the apertures 52 pass` through the slots 58 adjacent to the other end of the muffler. This construction, consequently, divides each pressure pulse into two decidedly different parts which pass in paths of different length through the interior of the mufller, one part of the pressure pulse passing through the opening 51 into close proximity of the inlet opening of the discharge conduit 59, while the other part of the gas pulse discharging through the openings 58 must travel through the greater portion of the length of the muffler before it can pass into the inlet of the discharge. conduit 59. By means of this arrangement, the two parts of each gas pulse are very decidedly out of phase with each' Except as herein described, the otherl other. parts of the muffler shown in Figs. 5 and 6 are very similar to those employed in the muler shown in Figs. 1 to 4.

In the modified construction shown in Fig. 7, an inlet conduit 65 is provided having two groups of perforations B6 and 61, which are surrounded by an intermediate shell 68 suitably secured to the conduit 65 by means of transverse baffles 69 and 1B. The rear end of the intermediate shell is open so that gases discharged through the apertures 61 may pass through the open end of the intermediate shell toward the rear end of the muffler. The portion of the intermediate shell 68 between the baffles 69 and 10 is provided with a series of openings or perforations 'l2 through which those gases and sound waves are discharged which have entered the intermediate shell through the perforations 66 of the inlet conduit. The perforations 12 break lup that part of each gas pulse which passes through the apertures 66 of the inlet conduit into a large number of different parts discharged at different intervals lengthwise of the inlet conduit and all of these apertures 'l2 are spaced'at a distance from the open rear end of the intermediate shell 68, so that a breaking up of the gas impulses into a number of separate parts also results from/this construction. In the construction shown in Fig. 7, the discharge conduit 'I4 has its open end 15 extending substantially perpendicular to the length of the conduit and .is provided with a comparatively large group of perforations 'i6 to facilitate the entrance of gases and sound waves into the discharge conduit I4. Otherwise the muffler shown in Fig. 7 is similar in construction and operation to those hereto- Vfore described.

The'modified construction of the inlet unit shown in Fig. 8 differs from that shown in Fig. 7, in that the inlet conduit 80 is provided with three groups of perforations or openings 8|, 82 and 83 which are surrounded by an intermediate shell 84 supported from the conduit 80 by means of transverse walls or baffles 85 and 85 which are spaced from the opposite ends of the intermediate shell 84. Consequently, the gases discharged through the group of apertures 8| pass out into the space within the muffler housing through the open front end of the intermediate shell 84 and the gases discharged through the apertures 83 pass out through theopen rear end of this intermediate shell. The annular space between the conduit 80 and intermediate shell 84 and between the ballles 85 and 83 forms a resonator chamber which may advantageously be used to silence certain sounds in the exhaust.

The inlet and discharge units of the muffler may be arranged and secured to the outer shell of 'the housing of the muffler in any suitable or desired manner. This outer shell may also be of any desired shape, that shown being of approximately circular cross section. The outer shell may be of greater diameter than the comhined diameters of the intermediate shells arranged about the inlet and discharge conduits, in which case, the discharge conduit may be arranged at one side of the vertical central plane ol' the outer shell, as clearly shown in Figs. 2 and 6.. This arrangement of the inlet and discharge units in the outer shell makes it possible to use mulers embodying this invention,

to replace return iiow muillers of the type having three conduits, one of which carries the gases from the rear to the front end of the muler. The arrangement shown in Figs. 2` and 6 also provides for a large volume within the housing ol the muler for equalizing pressure pulses and for destroying low frequency sound waves. The intermediate shells are preferably welded to each otherat their line of contact and each intermediate shell is preferably also welded to the outer shell. thus forming a strong and rigid muffler construction. v

The mufflers shown in the drawings are of sirnplied construction, in that they omit entirely the return tube commonly employed in reverse flow mulllers which carries the gases from the rear to the front end of the muffler and the omission of this tube makes possible the discharge ol' gases from the inlet passage at different intervals lengthwise of the conduit and their eX- pansion in the relatively large interior of the housing. The 'construction described also provides a larger expansion chamber between the inlet and discharge units, which results in a treatment of the gases and sound waves in the muffler in such a manner that they are acted upon by the high frequency acoustic train associated with the discharge conduit with very much greater eiciency than in mulilers in which a third or reverse ow conduit is employed.

It-will be noted that in niulers constructed in accordance with this invention, a very rapid evening out of the rate of fluctuations of pressure results in the muffler, and also ilow of gases through the muiller results with the minimum of turbulence, so that back pressure is kept 10W by avoiding turbulence, as well as by evening out the iiow of gas through the discharge conduit and tail pipe.

We claim as our invention:

1. A muiiler including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit in said housing and connected respectively with said inlet and said discharge and having portions thereof longitudinally coextensive with each other, the volume of said housing being materially greater than the combined volume of said conduits, and the space in said housing enclosing said coextensive portions being substantially' unobstructed, said discharge conduit having its open end arranged near the end of the housing remote from said discharge, and said inlet conduit being provided with a plurality of openings'at different distances from the opening of said discharge conduit and out of which gases flow from said inlet conduit into the interior of said housing to said open end of said discharge conduit, whereby parts of gas impulses discharged through said openings must travel through different distancesl in said housing to reach the opening in said discharge conduit.

2. A muiiler including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit andv a discharge conduit in said housing and connected respectively with said inlet and said discharge and having portions thereof 'longitudinally coextensive with each other, the volume of said housing being materially greater than the combined volume of said conduits, and-the space in said housing enclosing l, said coextensive portions being substantially unobstructed, said discharge conduit having its open charged through said openings in said inlet conduit into different parts of said housing located at different distances from the open end of said discharge conduit.

3. A muler including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit in said housing and connected respectively with said inlet and said discharge and arranged in substantially parallel relation to each other, the volume of said housing being materially greater than thecombined Volume of said conduits, said discharge conduit having its open end arranged near the end of the housing remote from said discharge and said inlet-conduit being provided with a plurality of openings at different distances from the opening of said discharge conduit and out of Which gases flow from said inlet conduit through the interior of said housing, to said open end of said discharge conduit, the portion of said housing enclosing said conduits being substantially unobstructed, whereby parts of gas impulses Vdischarged through said openings must travel through diierent distances in said housing to reach the opening in said discharge conduit, said discharge conduit being provided with perforate portions, and an imperforate shell enclosing perforate portions of said discharge conduit to form therewith a high frequency acoustic chamber.

4. A muliler including a housing having an inlet a at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit in said housing and connected respectively with said inlet and said discharge and arranged in substantially parallel relation to each other, the volume of said housing being materially greater than the combined volume of said conduits, said discharge conduit having its open end arranged near the end of the housing remote from said discharge and said inlet conduit being provided with a plurality of openings at different distances from the opening of said discharge conduit and out of -which gases ow from said inlet conduit through the interior of said housing, to said open end of said discharge conduit, the portion of said housing enclosing said conduits being substantially unobstructed, whereby parts of gas impulses discharged through said openings must travel through different distances in said housing to reach the opening in said discharge conduit,

'fil

said discharge conduit;l being provided with perforate portions, and an imperforate shell enclosing perforate portions .of said discharge conduit to form therewith a high frequency acoustic chamber, saiddischarge conduit having a restricted portion to retard the iiow of gases therethrough.

5. A muler including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit in said housing and connected respectively with said inlet and said discharge and having longitudinally coextensive portions in said housing, said discharge conduit having its open end arranged near the end of the housing remote from said discharge and said inlet conduit being provided with a plurality of openings at different distances .from the opening of vsaid discharge conduit and out of which gases flow from said inlet conduit through the interior of said housing, to said open end of said discharge conduit, the portion of said housing enclosing said conduits being substantially unobstructed, whereby parts of gas impulses discharged through said openings must travel through different distances in said housing to reach the opening in said discharge conduit, said discharge conduit being provided with perforate portions, a shell enclosing perforate portions of said discharge conduit to form therewith a high frequency1 Aacoustic chamber, and a restriction in said discharge conduit arranged between said perforate portions.

ii` A muler including a housing having an inlet at one end and a discharge at the other end thereof, an inlet unit in said housing including a conduit connected with said inlet and having openings arranged at intervals lengthwise thereof throughLwhich gases pass from said conduit into said housing and sheet metal members arranged about said openings in said conduit and having openings for discharging gas into said housing about said inlet unit to prevent gases discharged through said openings from impinging directly on said housing, a discharge unit arranged in said housing and including a discharge conduit connected with said discharge and having an opening to receive gases from said housing and having4 a perforate portion, and a substantially imperforate shell surrounding said perforate portion to form a high frequency acoustic chamber,

the entire interior of said housing not occupied by said units serving as an expansion and equalizing chamber through which'v gases and sound waves pass in paths of different lengths from said openings in said inlet unit to said discharge unit and being substantially unobstructed to permit free iiow lof gases in said housing from said inlet unit to said outlet unit.

7. A muflier including a housing having an inlet at one end and a discharge at the other end thereof, an inlet unit in said housing including a conduit connected with said inletand having openings arranged at intervals lengthwise thereof through which gases pass from said conduit into said housing and sheet members arranged about said openings in said'conduit to prevent gases discharged through said openings from impinging directly on said housing, and a discharge unit arranged in said housing and including a discharge conduit connected WithY said discharge and having an opening to receive gases from said housing and having a perforate portion, and a substantially imperforate shell surrounding said perforate portion to form a high frequency acoustic chamber, the entire interior of said perforations in a'portion thereof adjacent to its open end beyond its shell, whereby gases and sound Waves from said housing may pass into the open end and into said last mentioned perforations.

8. A muiiier including a housing having an inlet at one end and a discharge at the other end thereof, an inlet unit in said housing including a conduit connected with said inlet and having perforations throughout a substantial portion of the length thereof, said inlet unit also including a shell arranged about said perforations against which gases discharged through said perforations may impinge and having openings arranged vat intervals lengthwise thereof through which gases pass into said housing, and a discharge unit including a conduit connected with said discharge and having a gas receiving opening in said housing which is arranged at different distances from said openings in said shell, said units having longitudinally coextensive portions in said housing, the portion of said housing enclosing said coextensive portions being substantially unobstructed to permit gases to flow through paths of different lengths through said housing from said inlet unit to said opening of said discharge conduit.

9. A muiller including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit connected respectively with said inlet and discharge and having longitudinally coextensive portions in said housing and provided with perforations extending throughout a substantial portion of the length of each conduit, a shell arranged Within said housing about the perforate portion of said inlet conduit and having openings out of which gases may pass into said housing at different distances lengthwise of said shell, and a second shell which is substantially imperforate and which is arranged about and encloses a perforate portion of said discharge conduit to form therewith a high frequency acoustic train, said discharge conduit having a gas receiving opening at the end thereof arranged at different distances from said openings in said iirst mentioned shell, said shells being secured to each other and to said housing, vthe portion of said housing enclosing said coextensive portions being substantially free from obstructions to permit gases to flow freely through paths of different lengths through said housing from said inlet unit to said opening in said discharge conduit.

l0. A muier'including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit connected respectively with said inlet and discharge and having longitudinally coextensive portions in saidhousing and provided with perforations extending throughout a substantial portion of the length of each conduit, a shell arranged within said housing and about the perforate portion of said inlet conduit and having openings through which gases may pass into said housing at different distances lengthwise of said shell, and a second substantially imperforate shell arranged about and enclosing a perforate portion of said discharge conduit to form therewith a high frequency acoustic train, the end of said discharge conduit opposite to the end thereof connected with said discharge being open and being arranged at different distances from said openings in said first shell and provided adjacent said open end with perforations into which gases and sound waves from said housing may pass.

11. A muffler including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit in said housing and connected respectively with said inlet and said discharge and arranged in substantially parallel relation to each other, said discharge conduit having an opening adjacent to the inlet end of said housing and said inlet conduit having an opening intermediate of the ends thereof and having its end nearest to the discharge end of said housing substantially closed, and an intermediate shell arranged about said opening of said inlet conduit and receiving gas discharged from said opening in said inlet conduit and having a plurality of discharge openings through which gases pass into said housing, said openings of said intermediate shell being arranged at different distances from the opening of said discharge conduit to cause different portions of gas pulses entering said housing to travel through different distances to the opening of said discharge conduit.

12. A muier including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit in 'said housing and connected respectively with said inlet and said discharge and having longitudinally coextensive portions, said discharge conduit having an opening adjacent to the inlet end of said housing and said inlet conduit having an opening, intermediate of its ends and having its end adjacent to the discharge end of said housing substantially closed, an intermediate shell arranged Within said housing about said opening of said inlet conduit and receiving gas discharged from said opening in said inlet conduit, transverse baffles connecting the end portions of said intermediate shell with said inlet conduit and provided With openings through which gases pass from said intermediate shell into said housing at different distances from the opening in said discharge conduit.

13. A muffler including a housing having an inlet at one end and a discharge at the other end thereof, an inlet conduit and a discharge conduit in said housing and connected respectively With said inlet and said discharge and having longitudinally coextensive portions, said discharge conduit having an opening adjacent to the inlet end of said housing and said inlet conduit having apertures arranged at intervals lengthwise thereof, an intermediate shell arranged about said apertures, transverse baffles connecting said intermediate shell and said inlet conduit, and forming with said-shell and conduit a high frequency resonator chamber communicating with some of said apertures, said intermediate shell also covering apertures of saidinlet conduit located at opposite sides of said baiiles and having openings at opposite ends thereof to disch arge gases into said housing.

14. A muffler including a housing having an inlet at one end thereof and an outlet at the other end thereof, a conduit in said housing receiving gases from said inlet and having perforations arranged at intervals lengthwise thereof, through which gases and sound waves are discharged, a second conduit in said housing and connected with said outlet and having a portion coextensive with saidqrst mentioned conduit and having an opening for receiving gases andA sound waves from the interior of said housing, and an imperforate shell extending about said perforations 'of said rst conduit and having open ends through which gases and sound waves may pass into different portions of said housing located at different distances from said opening of said second conduit, the portion of said housing enclosing said coextensive portions of said conduits being substantially unobstructed to permit gases to flow freely through said housing from the open ends of said shell to said opening in said seco-nd conduit.

15. A muffler including a housing having an inlet at one end and a discharge at the other end thereof, a conduit in said housing receiving gases from said inlet at one end thereof and having its other end substantially closed, a second conduit in said housing having a portion thereof arranged enclosing said coextensive portionsof said con-- duits forming a substantially unobstructed space, through which gases discharged from different openings in said rst conduit travel through different distances in said housing in passing from said openings to the inlet in said second conduit.

16. A muffler including a housing having an inlet at one end and a discharge at the other end thereof, a conduit in said housing receiving gases from said inlet at one end thereof and having its other end substantially closed, a second conduit in said housing having a portion thereof arranged longitudinally coextensive with a portion of said first mentioned conduit, said rst mentioned conduit having openings arranged at different distances lengthwise thereof in the coextensive portion thereof and out of which gases are disrst conduit, the portion of said housing enclosing said coextensive portions of said conduits forming a substantially unobstructed space, to Cause gases disch-arged from different openings in said first conduit to travel through different distances in said housing in passing from said openings to the inlet in said second conduit, said second conduit also having perforations near the open inner v end, thereof and opening into said space to enable gases and sound Waves from the interior of said housing to pass into said conduit through the open end thereof and through said perforations.

17. A muflier including a housing forming a chamber having an inlet at one end and a discharge at the other end thereof, a pair of conduits in said chamber having portions thereof longitudinally coextensive with each other, one of said conduits being connected with said inlet and the other conduit with said discharge, both of said conduits having openings therein communicating with the interior of said chamber to permit gases to flow out of an opening in said inlet conduit through said chamber and into an opening in said outlet conduit, one of said conduits having a plurality of openings of approximately the same size .lll

arranged at dllerent distances from an opening lengths will be out of phase with each other when. in the other of said conduits, whereby substanpassing through said conduit connected with seid tlally equal streams of gases passing through discharge.

said chamber from one conduit to another travel LUTHER GRANT HECTUR. in paths which differ in length, whereby gas pul- HOWARD L. SCHULTZ; sations travelling in seid paths of different 

